Brain Spinal cord Central nervous system (CNS) Peripheral nervous system (PNS) Figure 22.1 The human nervous system.
The Nervous System Meninges protect brain and spinal cord Dura mater: outermost layer Arachnoid mater: middle layer Subarachnoid space contains cerebrospinal fluid (CSF) Pia mater: innermost layer Blood–brain barrier
Figure 22.2 The meninges and cerebrospinal fluid. Skull bone Cerebrum Cerebellum Spinal cord Subarachnoid space of spinal cord Subarachnoid space (contains cerebrospinal fluid) Skull bone Dura mater Arachnoid mater Pia mater Blood vessel Cerebrum Cranial meninges Dura mater Arachnoid mater Pia mater Spinal meninges Subarachnoid space (contains cerebrospinal fluid) Central canal
The Nervous System Meningitis: inflammation of meninges Encephalitis: inflammation of the brain Meningoencephalitis: inflammation of both
Bacterial Meningitis Initial symptoms of fever, headache, and stiff neck Followed by nausea and vomiting May progress to convulsions and coma Diagnosis by Gram stain and latex agglutination of CSF
Figure 22.4 Spinal tap (lumbar puncture). Spinal cord Spinal needle is inserted, usually between the fourth and fifth lumbar vertebrae Fourth lumbar vertebra Cauda equina Sample of cerebrospinal fluid Fifth lumbar vertebra L4 L5 Cerebrospinal fluid Longitudinal section of the spine
Haemophilus influenzae Meningitis Occurs mostly in children (6 months to 4 years) Gram-negative aerobic bacteria, normal throat microbiota Capsule antigen type b Prevented by Hib vaccine
Neisseria Meningitis Also called meningococcal meningitis Caused by N. meningitidis Gram-negative, aerobic cocci with a capsule 10% of people are healthy nasopharyngeal carriers Begins as throat infection, rash Serotypes B, C, Y, W-135 Serotype B & C in United States Serotype A in Africa Vaccination (A, C, Y, W-135 capsule) recommended for college students
Figure 22.3 Neisseria meningitis. Cilia N. meningitidis
Streptococcus pneumoniae Meningitis Also called pneumococcal meningitis Caused by S. pneumoniae (a gram-positive diplococcus) 70% of people are healthy nasopharyngeal carriers Most common in children (1 month to 4 years) Mortality: 30% in children, 80% in elderly Prevented by vaccination
Listeriosis Caused by Listeria monocytogenes Gram-negative aerobic rod Usually foodborne; it can be transmitted to fetus Reproduce in phagocytes Spread phagocyte-to-phagocyte
Figure 22.5 Cell-to-cell spread of Listeria monocytogenes, the cause of listeriosis. Listeria monocytogenes Macrophage Pseudopod Macrophage
Diseases in Focus: Meningitis and Encephalitis. Gram stain of cerebrospinal fluid.
Tetanus Caused by Clostridium tetani Gram-positive, endospore-forming, obligate anaerobe Grows in deep wounds Tetanospasmin released from dead cells blocks relaxation pathway in muscles Prevention by vaccination with tetanus toxoid (DTaP) and booster (Td) Treatment with tetanus immune globulin (TIG)
Advance case of tetanus
Botulism Caused by Clostridium botulinum Gram-positive, endospore-forming, obligate anaerobe Intoxication comes from ingesting botulinal toxin Botulinal toxin blocks release of neurotransmitter, causing flaccid paralysis Prevention Proper canning Nitrites prevent endospore germination in sausages
Botulism Treatment: supportive care and antitoxin Infant botulism results from C. botulinum growing in intestines Wound botulism results from growth of C. botulinum in wounds
Botulinal Types Type A toxin 60–70% fatality Found in CA, WA, CO, OR, NM Type B toxin 25% fatality Europe and eastern United States Type E toxin Found in marine and lake sediments Pacific Northwest, Alaska, Great Lakes area
Leprosy Also called Hansen’s disease Caused by Mycobacterium leprae Acid-fast rod that grows best at 30°C Grows in peripheral nerves and skin cells Transmission requires prolonged contact with an infected person
Leprosy Tuberculoid (neural) form: loss of sensation in skin areas; positive lepromin test Lepromatous (progressive) form: disfiguring nodules over body; negative lepromin test
Figure 22.9 Leprosy lesions. Tuberculoid (neural) leprosyLepromatous (progressive) leprosy
Poliomyelitis (Polio) Poliovirus Transmitted by ingestion Initial symptoms: sore throat and nausea Viremia may occur; if persistent, virus can enter the CNS Destruction of motor cells and paralysis occurs in <1% of cases Prevention: vaccination (enhanced-inactivated polio vaccine)
Figure Worldwide annual incidence of poliomyelitis. Number of confirmed polio cases Year ,000 2,000 3,000 4,000 5,000 6,000 7, ,000 2,000
Rabies Caused by the rabies virus Transmitted by animal bite Furious rabies: animals are restless, then highly excitable Paralytic rabies: animals seem unaware of surroundings
Figure Pathology of rabies infection. Virus enters tissue from saliva of biting animal. Virus replicates in muscle near bite and enters neuron of peripheral nervous system. Virus moves up peripheral nervous system to CNS. Virus ascends spinal cord. Virus reaches brain and causes fatal encephalitis. Virus enters salivary glands and other organs of victim.
Figure Reported cases of rabies in animals. Skunk Fox Raccoon Fox and skunk KEY Areas of the United States in which rabies predominates in certain wildlife species. Rabies-infected bats were reported in 47 of the 48 contiguous states. In eastern states in which raccoons are the predominant rabies-infected animal, many cases were also reported in foxes and skunks.
Figure Reported cases of rabies in animals. KEY Rabies cases in various wild and domestic animals in the United States. Rabies in domestic animals such as dogs and cats is uncommon because of high vaccination rates. Raccoons, skunks, and bats are the animals most likely to be infected with rabies. Most human cases are caused by bites of bats. Worldwide, most human cases are caused by bites of dogs. Raccoons Bats Skunks Foxes Cats Dogs Cattle Horses/mules Wild Domestic 35.5% 24.8% 24.5% 7.7% 4.6% 1.2% 1.1% 0.6%
Clinical Focus: A Neurological Disease, Figure B. Silver-haired bat.
Rabies Virus Virus multiplies in skeletal muscles and then brain cells, causing encephalitis Initial symptoms may include muscle spasms of the mouth and pharynx and hydrophobia
Prevention of Rabies Preexposure prophylaxis: injection of human diploid cells vaccine (HDCV) Postexposure treatment: vaccine plus rabies immune globulin (RIG)
Cryptococcus neoformans Meningitis Also called cryptococcosis Soil fungus associated with pigeon and chicken droppings Transmitted by the respiratory route; spreads through blood to the CNS Mortality up to 30% Treatment: amphotericin B and flucytosine
Figure Cryptococcus neoformans. Capsule
Chronic Fatigue Syndrome Also called myalgic encephalomyelitis (ME) Unexplained fatigue that lasts at least 6 months, plus four of these symptoms: Sore throat Tender lymph nodes Muscle pain Pain in multiple joints Headaches Unrefreshing sleep Malaise after exercise Impaired short-term memory or concentration
Chronic Fatigue Syndrome Experimental treatment promotes antiviral interferons